Fig. 5.

The reciprocal tolerance induction of the two immune competent cell populations during the first 60 days of passenger leukocyte migration that explains the nonessential role of HLA matching in organ transplantation. Cytoablation of the human bone marrow recipient (e.g., with supralethal irradiation) removes the host arm of the immune interaction, leaving the patient dependent on HLA matching for avoidance of GVHD. The nullification effect of the coexisting donor and recipient cells also explains why lymphoid-rich organs seldom cause GVHD.